In the field of gas turbine engines, and in particular ducted-fan gas turbine engines, it is known to provide fan track liners inside the fan case of the engine, which surrounds the propulsive fan at the front of the engine. Fan track liners typically comprise an abradable liner which is supported by an aluminium honeycomb structure. The abradable liner usually consists of Nomex honeycomb which is filled with a lightweight epoxy filler. This liner forms an aerodynamic seal between the tips of the fan blades and the fan case to minimize leakage of air over the tip of the fan blades. Such leakage needs to be avoided or mitigated because it affects the performance and stability of the fan blades. Under certain operating conditions, it is acceptable for the fan blades to make contact with the abradable liner. The depth of the liner is determined by the orbiting radius of the fan blade assembly following a fan blade failure.
Conventional fan track liners usually have a multipart design which comprises a plurality of separate liner panels which are installed in side-by-side relation around the inner surface of the engine's fan case. A concern with a segmented arrangement is that there can be a number of small gaps between adjacent panels of the liner which can affect the long term integrity of the liner because, for example, they can provide paths for water ingress which can undermine the integrity of the bond formed between the liner and the engine's fan case. Furthermore, circumferential gaps between circumferentially adjacent panels can present steps around the fan track liner which can affect the release trajectory of a fan blade in the event that it becomes detached from the fan.
Conventionally, fan track liner panels are bonded to the engine's fan casing. This has the disadvantage that it makes removal of the panel from the casing difficult. A further problem is that removal of a panel which is securely bonded to the fan casing can cause damage to the fan casing. Whilst a metal fan casing may be able to withstand the forces applied to it during removal of a bonded fan track liner, composite fan casings which are now becoming favoured have much lower tolerance to damage arising during removal of a fan track liner, and which might result in the formation of scratches in the fan casing by chipping away the bonding material used to bond the fan track liner to the fan casing.